A variety of methods can be utilised to control fluid loss at shafts, rods or valve stems, all of which require some freedom of movement in order to be able to operate effectively. The oldest, and still most commonly used of these dynamic sealing devices is the packing (often termed compression packing - so called because of the manner in which it performs the sealing function). Usually made from relatively soft, pliant materials, packings consist of a number of rings which are inserted into the annular space (stuffing box) between the rotating or reciprocating shaft and the body of the mixer, pump or valve. By tightening a follower or gland against the outboard ring, pressure is transmitted to the packing set, expanding the rings radially against the side of the stuffing box and the shaft, so effecting a seal.
Packings
find their major use in the utilities and process industries, such as petrochemical,
chemical, pulp and paper, steel mills, water, sewage, food, power generation. They are
used to seal all types of fluids over a wide range of temperatures and pressures. Packings
are used in rotary, centrifugal and reciprocating pumps, mixers, agitators, dryers, valves
and many other types of mechanical equipment. In particular, they are the most popular
sealing technology for valves.
When used in continuously rotating or reciprocating equipment, efficient operation normally depends on a fluid film between the surface of the shaft and the packing. This film acts as a lubrication, and can result from:
lubricants built into the packing controlled leakage of the process medium an external lubricant supply combination of the above
Packings are made from various materials in a variety of shapes, sizes and constructions, dependent upon the service requirements. Despite the introduction of more modern sealing technologies, packings continue to be a major choice for users because they are extremely cost-effective, relatively easy to install and maintain. With proper attention, a high degree of successful operation can be anticipated.
See ... List of Division Members
As expected, the Members of the ESA Packings Division supply an extremely wide range of packings materials, for use in thousands of applications world-wide.
Despite
these variety of applications, much of the attention of the Division has been focused on
the challenge of leakage from valves, most of which are sealed by packings technology.
This relates to the reports that around 50% of fugitive emissions on petrochemical or
chemical sites come from leaking valves.
Consequently, the ESA Packings Division commissioned a valve emission test programme, awarded jointly to two independent test institutes, the initial results of which were reported at the Conference in Antwerp. The ESA is now collaborating with the valve industry and end users on the next stage in this programme, which is a project supported by the European Commission under the Standards, Measurement and Testing protocol. The key objective of this project is to improve and standardise valve emission test methods for both manufacturers and users ( ... see SMT Project). Once again, the initial reports of this work were reported at the Conference in Düsseldorf.
Sealing Technology BAT guidance note
Sealing technology is involved in virtually all of the sectors covered by the EU IPPC
Directive. Yet, only limited information and guidance on sealing options is
available in most of the BREF notes which have been published to date. For this reason,
the ESA has produced a Sealing Technology BAT
guidance note, with sections covering the best available techniques
for sealing solutions required to meet the IPPC legislation.
